I know this is a quite old thread, but I faced the same issues on Windows when I try to use the class 1 USB (i2o2 or i8o2 configurations). I am using software 6.15.2rc1.When the firmware is tested on a Mac or an iPad, it works (including High Sierra), they both report a correct number of audio channels and any audio application is able to stream audio to XK216 output.When tested on WinXP, Win7 and Win10 machines, it is impossible to get any sound on audio outputs (system sounds or sounds coming from any application).After applying the patch from Ross, it works immediately on the XP and Win7 machines, but I noticed a strange issue : I had to set the output level to the max in Windows, other wise the sound is almost muted by default (I noticed I had a very faint sound almost by accident, I thought the firmware was still not working)On Windows 10, I had to do one more thing before the XK216 could work properly. I needed to remove manually the device from the driver list, then tell Windows to scan for new devices. And now it works.So I confirm that the UAC "trick" is necessary to make the class 1 work correctly on Windows machine.So XMOS should probably add it in the software package, this would probably help others to save time to investigate on that issue (lost two days of work before I find the explanation here °-)